It appears that in training that combines both aerobic and resistance exercises, performing a comparatively higher intensity resistance exercise first would augment fat utilization and energy expenditure during subsequent aerobic exercise.

Chris, since you had originally posted on Lyle McDonald's book back in April of 2008, I'm curious to know how effective you feel his recommended protocol is. Have you tried it/them and how are the results?

Seems like I'm stuck at the 9-10% body fat range, but would like to drop another percentage point or so.

It has been known for a long time that aerobic exercise uses a lot of carbohydrate for fuel, especially in the initial time period. I am looking at a graph from Noakes' book "The Lore of Running" which shows that in endurance trained cyclists, the percent of energy contributed from muscle glycogen when exercising at only 70% VO2max is 60-70% for the first hour of exercise. About 20% energy is supplied by fat, and another 10% from blood glucose. By 2-3 hours of continuous exercise, the muscle glycogen contribution has only fallen to 40-50%, while the fat has increased to ~30% (more glucose from the liver is also being utilized). In less well trained people, the carbohydrate contribution would be even greater, since they are not well adapted to fat burning yet. Of course, at higher exercise intensity, the contribution of fat would be even lower or zero. It is also well known that as the muscle glycogen stores get lower and lower, more fat oxidation occurs. It does take quite a bit of aerobic exercise to burn significant fat, but of course higher intensity exercise burns even less. I doubt very many people do enough intervals or resistance exercise to even come close to depleting glycogen enough to favor fat metabolism. But burning off sugar is good by any means. :)

So this study you cite is consistent with the idea that as muscle glycogen is depleted, more fat oxidation must occur during subsequent aerobic exercise. And even a little exercise at low intensity will cause the muscles to express Glut4 transporters to refill their glycogen stores, thereby lowering blood glucose levels, which should be a good thing.

Would it depend how much glycogen is in the body ready to be used and how much is used by strength training? If you still have enough glycogen to cover the expenditure of a subsequent aerobic workout, then nothing has been accomplished, right? Noob here. Excuse me :)

I have read in some book that the body can store up to 2500 calories of glycogen. Is that typical at any given time?

from what I recall from Lyle's book it is all about liberating fat form the cells then burning it. Intervals or resistance work is good at liberating the fat from the cells but not at burning it. FOr that you need the aerobic stuff which follows. So it is intervals to get the fat out then steady state stuff to burn it so it doesn't just go back to the fat cells. It is worth getting the book